Abstract:
Background: Diabetes mellitus, a chronic metabolic disorder affecting millions of individuals worldwide, is associated with a multitude of complications, including diabetic kidney disease (DKD). Despite numerous choices of hypoglycemic agents use for diabetes management, DKD remains a significant health burden. Among the various agents investigated for their potential reno-protective effects is the glucagon like peptide-1 receptor agonist (GLP-1RA), liraglutide. GLP-1RAs are primarily used in the management of type 2 diabetes, and their reno-protective mechanisms are not well defined. Furthermore, the beneficial effects of GLP-1RAs in type 1 diabetes and their action on kidney function remain understudied. Recent evidence highlights the crucial role of the immune system in DKD, with macrophages being implicated in the initiation and progression of the disease. Furthermore, extensive data from our group and others have shown that reactive oxygen species (ROS) overproduction and calcium signaling dysregulation also play a crucial role in the progression of the disease. We hypothesize that the mechanism behind inflammatory deregulation is macrophage polarization towards an M1 pro- inflammatory phenotype instead of an M2 anti-inflammatory phenotype. This is associated with increased ROS production and calcium signaling alteration. Consequently, this study aims to investigate the mechanism behind the reno-protective effect of liraglutide in a type 1 diabetic animal model and to elucidate its effect on macrophage polarization by modulating NADPH oxidase - TRP crosstalk. Materials and methods: Adult male Sprague Dawley rats as well as C57/BL6J mice were divided into three groups: a control group (C), an STZ-induced insulin deficient animal model group mimicking type 1 diabetes, T1D (D), and a T1D group treated with subcutaneous injections of liraglutide at a dose of 0.3mg/kg twice daily (DL) for8 and 13 weeks period. Following treatment, renal function studies were performed after which mice were sacrificed and the 2 kidneys removed for histopathological, biochemical, and molecular analyses. Results:
Liraglutide treatment significantly improves diabetes-induced kidney injury despite the sustained high glucose levels, by reducing renal hypertrophy, decreasing blood urea nitrogen (BUN) levels, serum creatinine (sCr), urinary albumin to creatinine ratio (ACR), and proteinuria. Histopathology analysis shows reduced glomerular hypertrophy, decreased glomerulosclerotic index, and reduced collagen deposition. These functional changes were paralleled by a normalization of fibronectin, collagen IV, WT1, nephrin and podocin expression. Besides, liraglutide treatment decreases mRNA levels and protein expression of general inflammatory cytokines, as well as specific markers of M1 macrophage phenotype. Conversely, there was an increase in the mRNA and protein levels of anti-inflammatory cytokines, along with an increase in markers of M2 macrophage phenotype. Besides, liraglutide treatment attenuates ROS overproduction, as evidenced by the reduction of NADPH oxidase activity in mice kidney biopsies. In addition, liraglutide treatment restores the expression of TRPM2 and TRPC6 cation channel expression to near normal levels. Conclusion: To the best of our knowledge, this is the first study to show an anti-inflammatory reno-protective effect of liraglutide in T1DM manifested by a shift in macrophage polarization from the M1 inflammatory phenotype to the M2 anti-inflammatory phenotype associated with a modulation of the NADPH-TRP crosstalk.